fixing bug where schema existance is not properly checked for some postgres isntallations

I ran into an issue when I setup Phinx with my Postgres DB. For some reason my information_schema.schemata table is empty, so when Phinx tries to check if a schema exists, it incorrectly said it did not. I tried uninstalling Postgres and reinstalling and the issue remained. I did some research and found that there is a more direct way to check if a schema exists, http://stackoverflow.com/a/13877950. When using the query he listed, Phinx worked fine for me. I don't think this is a common issue but one that some people might run into.